A cover or lid, which is composed of a ferromagnetic material, can be punched and/or deep drawn from the ferromagnetic sheet material thereby providing it with a circumferential supporting lip, scoring or punching out or in the surface of the cover or lid to form a tear-out opening, and coating the cover or lid completely with a lacquer, varnish or paint coating. In the case of punching out the tear-out opening the cover or lid is equipped with a covering sealed tear-off foil, preferably a plastic-aluminum foil.
In making a tear-out cover according to the above process the lacquer or varnish coating of the cover or lid is provided by applying the lacquer or varnish to both sides of a blank and subsequently the blank is provided with the supporting lip and is scored and/or the surface is punched in or out. When, instead of scoring to define the opening to be formed later, an opening is punched out, the subsequent closure of the tear-off opening could occur by sealing on a tear-off foil as previously mentioned.
However the shaping of the cover or lid after the lacquer or varnish coating of the blank requires a very flexible coating which during the required shaping of the blank does not tend to rip or peel off. Such lacquers are not always available or reliable.
Additional problems arise when the scoring and/or the punching in or out of the cover or lid surface occurs after the coating process. Particularly cut edges arise at the scored places or at the edges of the punched in or out openings which are especially susceptible to corrosion.
These covers or lids can only be used in a container for dry goods unless additional steps are taken to provide the endangered region with a corrosion resistant coating. For this purpose protection of these cut edges must be undertaken by either a subsequent coating process or an additional covering by an inner foil, that is, a foil applied in the container interior near the cover or lid.
A turning or folding over of the edges of the punched out opening is also possible so that these cut edges are on the outside of the cover when the cover closes the container and thus contact with the goods in the container is prevented.
However these outside cut edges are endangered by corrosion even when they are covered by the sealed on tear-off foil.